Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
  • G03H1/04—Processes or apparatus for producing holograms
  • G03H1/0443—Digital holography, i.e. recording holograms with digital recording means
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
  • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
  • G03H1/2294—Addressing the hologram to an active spatial light modulator
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
  • G03H1/04—Processes or apparatus for producing holograms
  • G03H1/08—Synthesising holograms, i.e. holograms synthesized from objects or objects from holograms
  • G03H1/0808—Methods of numerical synthesis, e.g. coherent ray tracing [CRT], diffraction specific
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
  • G03H1/04—Processes or apparatus for producing holograms
  • G03H1/08—Synthesising holograms, i.e. holograms synthesized from objects or objects from holograms
  • G03H1/0866—Digital holographic imaging, i.e. synthesizing holobjects from holograms
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
  • G03H1/0005—Adaptation of holography to specific applications
  • G03H2001/0033—Adaptation of holography to specific applications in hologrammetry for measuring or analysing
  • G03H2001/0038—Adaptation of holography to specific applications in hologrammetry for measuring or analysing analogue or digital holobjects
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
  • G03H1/04—Processes or apparatus for producing holograms
  • G03H1/0443—Digital holography, i.e. recording holograms with digital recording means
  • G03H2001/0447—In-line recording arrangement
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
  • G03H1/04—Processes or apparatus for producing holograms
  • G03H1/08—Synthesising holograms, i.e. holograms synthesized from objects or objects from holograms
  • G03H1/0866—Digital holographic imaging, i.e. synthesizing holobjects from holograms
  • G03H2001/0883—Reconstruction aspect, e.g. numerical focusing
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H2210/00—Object characteristics
  • G03H2210/30—3D object
  • G03H2210/33—3D/2D, i.e. the object is formed of stratified 2D planes, e.g. tomographic data
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H2226/00—Electro-optic or electronic components relating to digital holography
  • G03H2226/02—Computing or processing means, e.g. digital signal processor [DSP]
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H2240/00—Hologram nature or properties
  • G03H2240/50—Parameters or numerical values associated with holography, e.g. peel strength
  • G03H2240/56—Resolution

Definitions

• the present disclosure relates to lens-free imaging, and more particularly to reconstructing images from holograms.
• Lens-free imaging is a microscopy technique based on the principle of digital holography.
• digital holography a coherent light source (e.g., a laser) is used to illuminate the object specimen. As light passes through the specimen it is diffracted by the specimen, and the resulting diffraction partem is recorded by an image sensor such as a charge coupled device (CCD). After the resulting diffraction pattern has been recorded, an image of the specimen is reconstructed by post-processing the diffraction pattern by using a mathematical model of the diffraction process.
• CCD charge coupled device
• Holographic lens-free microscopy has several advantages over conventional microscopy. First, because there are no lenses in the system, the overall cost and physical size of the imaging system can be greatly reduced compared to traditional microscopes. Additionally, lens-free microscopy also allows much wider fields of view to be imaged than conventional microscope with equal magnification. Finally, because the image of the specimen is generated through postprocessing the recorded diffraction partem, there is no need for an operator to manually focus the system as the focal depth can be adjusted automatically through post-processing.
• Figure 1 depicts the diffraction of coherent light induced by an object as the light passes through the object.
• a coherent light source e.g., a laser
• the diffraction pattern would contain sufficient information to reconstruct a perfect image of the specimen at any desired focal depth.
• the full diffraction pattern of an object is a complex valued entity parameterized by both the amplitude and the phase of the electromagnetic wave at a given location in space (with the frequency of the wave assumed to be equal to the illuminating coherent light).
• imaging sensors such as a CCD
• imaging sensors are typically only capable of recording the amplitude of the diffraction pattern but not the phase.
• a significant portion of the information necessary to perfectly reconstruct the image of the specimen cannot be recorded, which manifests as significant artifacts when one attempts to reconstruct an image of the specimen with conventional approaches.
• traditional approaches to lens-free imaging typically only attempt to reconstruct an image of the specimen at a single focal depth, but if the specimen contains objects at multiple focal depths, then the diffraction from out-of-focus objects will corrupt the reconstructed images at a given focal depth.
• the presently-disclosed techniques address both of the above-described shortcomings of prior approaches— poor image reconstruction and limitation to a single focal depth— by utilizing a system and method to efficiently reconstruct images of a specimen from a recorded diffraction partem over potentially multiple depths of focus while simultaneously generating an estimate of the missing phase information.
• Using the disclosed technique results in significantly improved image quality over traditional image reconstruction techniques, allows for a three dimensional volume of the specimen to be reconstructed simultaneously, and provides a robust means of finding focal depths that contain objects, eliminating the need to manually tune focal depth.
• Figure 1 is an example of light diffraction induced by an object
• Figure 2 is a set of image reconstructions of a whole blood sample using different reconstruction algorithms showing both a large field of view (left) and a zoomed in portion of the image (right), where the top panels show images using a basic reconstruction algorithm and the bottom panels show images reconstructed using an embodiment of the present disclosure;
• Figure 3 is a chart showing a method according to an embodiment of the present disclosure;
• Figure 4 is a chart showing the magnitude of the reconstructed 3-dimensional volume over focal depth, where the y-axis shows the i x norms of the reconstructed images,
• Figure 5 is a diagram of a system according to another embodiment of the present disclosure.
• Figure 6 depicts local reconstruction of a hologram acquired by a system according to another embodiment of the present disclosure
• Figure 7 depicts remote reconstruction of a hologram acquired by a system according to another embodiment of the present disclosure.
• Figure 8 is a chart showing a method according to another embodiment of the present disclosure. DETAILED DESCRIPTION
• Holographic lens-free imaging is based on the principle of recording the diffraction pattern of light after it has passed through a specimen and attempting to invert the light diffraction process to reconstruct an image of the specimen.
• the recorded diffraction pattern does not contain sufficient information to adequately reconstruct an image of the specimen, and as result many existing reconstruction techniques suffer from substantial artifacts and degraded image quality.
• the present disclosure provides a technique to reconstruct holographic lens-free images with dramatically improved image quality over existing techniques and allows for the possibility of reconstructing images at multiple depths of focus simultaneously.
• Matrices are denoted with upper-case letters (X), vectors with lower-case bold letters ( ), and scalars with lower-case letters (x).
• the set of complex numbers is denoted as C, and the set of real numbers is denoted as Ji.
• x[i] denotes the z 'th entry of x.
• X[i,j] denotes the entry of X in the row and h column.
• ⁇ x The angle of a complex number x is denoted as ⁇ x
• ⁇ x ⁇ the amplitude is denoted as ⁇ x ⁇
• conjugate is denoted as x.
• ⁇ X ⁇ denotes an m x n matrix containing the absolute values of the entries of X
• ⁇ X denotes an m n matrix containing the angles of the entries of X
• X denotes an m x n matrix containing the conjugates of the entries of X.
• the holographic imaging process is based on the process of optical diffraction.
• a full review of diffraction theory is beyond the scope of this document, but a commonly used approximation which is very accurate for the typical distances used in holography is to model the diffraction process as a two-dimensional convolution.
• Xo the wavefront that will result from propagating that wavefront forward to a plane a distance z away, Xz, is given by the equation
• T(z) denotes a transfer function that models the diffraction of light over a distance z.
• T(z) denotes a transfer function that models the diffraction of light over a distance z.
• Various choices can be made for T(z) depending on the particular approximations one chooses in the model of the diffraction process (e.g., Fresnel, Huygens, far-field).
• the approximation used herein is the wide-angular spectrum (WAS) approximation, which defines the transfer function in the frequency domain as
• the linear operator is a unitary operator.
• the present disclosure may be embodied as a method 100 for holographic reconstruction of an image.
• the method 100 includes obtaining 103 a hologram.
• a reconstructed image and phase are generated 106 at a specified focal depth using an assumption of sparsity.
• the reconstructed image X and phase W can be generated 106 by solving 109 As described above, an
• the reconstructed image X and phase W is generated 106 by setting 112 initial values for the reconstructed image X, the estimated phase W, and the fit to background ⁇ .
• a Fourier transform of a transfer function ⁇ ( ⁇ ) is calculated 115, setting The background level is updated by calculating 118 as
• T he phase is u P dated b y calculating
• An updated Q is calculated 124 and the
• steps are repeated 130 for each of ⁇ , W, Q, and X to determine the reconstructed image.
• the steps may be repeated 130 for a predetermined number of times. The number of times may be determined manually by performing the above method 100 until the reconstructed image is of a desirable quality.
• the steps are repeated 130 until the change in the updated values of ⁇ , W, and/or X is less than a threshold in an iteration.
• the steps may be repeated 130 until the change in updated value of the reconstructed image is less than 10%, 5%, 3%, 2%, or 1%, or any other percentage value, in an iteration of the steps.
• the threshold value may be and percent change or an actual value. The threshold may be selected based on, for example, the quality of the reconstructed image balanced with the cost (e.g., computational time, etc.) of performing an additional iteration.
• the present disclosure may be embodied as a system 10 for lens-free imaging (see Figure 5).
• the system 10 has a processor 14 in communication with a lens-free image sensor 12.
• the system 10 may include a lens-free image sensor 12 for obtaining holographic images.
• the image sensor 12 may be, for example, an active pixel sensor, a charge-coupled device (CCD), a CMOS active pixel sensor, etc.
• the system 10 may further include a light source 16, such as a coherent light source.
• the image sensor 12 is configured to cooperate with the light source 16 to obtain a holographic image.
• the processor 14 is programmed to perform any of the methods of the present disclosure.
• the processor 14 may be programmed to operate the image sensor 12 to obtain a hologram and generate a reconstructed image and phase at a focal depth using an assumption of sparsity.
• the processor 14 may generate the reconstructed image by, for example, using an alternating minimization to update the phase, background level, and reconstructed image to solve eq. (7).
• the system 10 may be configured for "local" reconstruction, for example, where image sensor 12 and the processor 14 make up the system 10.
• the system 10 may further include a light source 16 for illuminating a specimen.
• the light source 16 may be a coherent light source, such as, for example, a laser diode providing coherent light.
• the system 10 may further include a specimen imaging chamber 18 configured to contain the specimen during acquisition of the hologram.
• the system 20 is configured for remote" reconstruction, where the processor 24 is separate from the image sensor and receives information from the image sensor through, for example, a wired or wireless network connection, a flash drive, etc.
• the processor may be in communication with and/or include a memory.
• the memory can be, for example, a Random- Access Memory (RAM) (e.g., a dynamic RAM, a static RAM), a flash memory, a removable memory, and/or so forth.
• RAM Random- Access Memory
• instructions associated with performing the operations described herein can be stored within the memory and/or a storage medium (which, in some embodiments, includes a database in which the instructions are stored) and the instructions are executed at the processor.
• the processor includes one or more modules and/or components.
• Each module/component executed by the processor can be any combination of hardware-based module/component (e.g., a field-programmable gate array (FPGA), an application specific integrated circuit (ASIC), a digital signal processor (DSP)), software-based module (e.g., a module of computer code stored in the memory and/or in the database, and/or executed at the processor), and/or a combination of hardware- and software-based modules.
• FPGA field-programmable gate array
• ASIC application specific integrated circuit
• DSP digital signal processor
• software-based module e.g., a module of computer code stored in the memory and/or in the database, and/or executed at the processor
• Each module/component executed by the processor is capable of performing one or more specific functions/operations as described herein.
• the modules/components included and executed in the processor can be, for example, a process, application, virtual machine, and/or some other hardware or software module/component.
• the processor can be any suitable processor configured to run and/or execute those modules/components.
• the processor can be any suitable processing device configured to run and/or execute a set of instructions or code.
• the processor can be a general purpose processor, a central processing unit (CPU), an accelerated processing unit (APU), a field-programmable gate array (FPGA), an application specific integrated circuit (ASIC), a digital signal processor (DSP), and/or the like.
• Some instances described herein relate to a computer storage product with a non-transitory computer-readable medium (also can be referred to as a non-transitory processor-readable medium) having instructions or computer code thereon for performing various computer- implemented operations.
• the computer-readable medium (or processor-readable medium) is non- transitory in the sense that it does not include transitory propagating signals per se (e.g., a propagating electromagnetic wave carrying information on a transmission medium such as space or a cable).
• the media and computer code also can be referred to as code
• code may be those designed and constructed for the specific purpose or purposes.
• non-transitory computer- readable media include, but are not limited to: magnetic storage media such as hard disks, floppy disks, and magnetic tape; optical storage media such as Compact Disc/Digital Video Discs (CD/DVDs), Compact Disc-Read Only Memories (CD-ROMs), and holographic devices; magneto-optical storage media such as optical disks; carrier wave signal processing modules; and hardware devices that are specially configured to store and execute program code, such as Application-Specific Integrated Circuits (ASICs), Programmable Logic Devices (PLDs), Read- Only Memory (ROM) and Random-Access Memory (RAM) devices.
• ASICs Application-Specific Integrated Circuits
• PLDs Programmable Logic Devices
• ROM Read- Only Memory
• RAM Random-Access Memory
• Other instances described herein relate to a computer program product, which can include, for example, the instructions and/or computer code discussed herein.
• Examples of computer code include, but are not limited to, micro-code or microinstructions, machine instructions, such as produced by a compiler, code used to produce a web service, and files containing higher-level instructions that are executed by a computer using an interpreter.
• instances may be implemented using Java, C++, .NET, or other programming languages (e.g., object-oriented programming languages) and development tools.
• Additional examples of computer code include, but are not limited to, control signals, encrypted code, and compressed code.
• This model is essentially the same as the model for reconstructing an image at a single focal depth as used in (7) but further extended to a full 3-dimensional volume.
• a hybrid algorithm can be used, where the hybrid algorithm utilizes alternating minimization to update the W and ⁇ variables and proximal gradient descent steps to update X. Additionally, most of the intermediate variables are left in the Fourier domain to facilitate the computation. The steps of the method are described in Method 2.
• Figure 4 shows the magnitudes of the reconstructed X t images as a function of the specified focal depth for 100 uniformly spaced focal depths over the range [650, 1150] microns. Note that the image depth with the largest magnitude corresponds to the focal depth that was found by manually focusing the depth of reconstruction, demonstrating how reconstructing images over a 3 -dimensional volume with the proposed method robustly and automatically recovers the focal depth of objects within the specimen.
• the present disclosure may be embodied as a method 200 for holographic reconstruction of images at a plurality of focal depths.
• the method 200 includes obtaining a hologram and generating 206 from the hologram a sequence of reconstructed images using an assumption of sparsity, wherein each image corresponds to a specified focal depth.
• the reconstructed images X t and phase W can be generated 206 by solving 209
• an approach to solving 209 eq. (13) is by using an alternating minimization to update the phase W and background level ⁇ and proximal gradient descent steps to update X.
• the background level is updated by calculating 218
• the phase is updated by calculating
• An updated G is calculated 224 by and an updated i? is calculated 227 by G— S.
• An updated image is calculated 230 for each image in the matrix of images according to an
• An update S is calculated 233 by
• the steps may be repeated 236 for a predetermined number of times. The number of times may be determined manually by performing the above method 200 until the reconstructed images is of a desirable quality.
• the steps are repeated 236 until the change in the updated values of ⁇ , W, and/or X t is less than a threshold in an iteration.
• the steps may be repeated 236 until the change in updated value of the reconstructed images is less than 10%, 5%, 3%, 2%, or 1%, or any other percentage value, in an iteration of the steps.
• the threshold value may be and percent change or an actual value. The threshold may be selected based on, for example, the quality of the reconstructed images balanced with the cost (e.g., computational time, etc.) of performing an additional iteration.

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• 2017
  • 2017-11-03 CN CN201780068070.2A patent/CN110352387B/zh active Active
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